If a solid sheet of metal were used the differences among the metals
might not be great.  However if you were to choose particulates there
would be a great difference.  Metallic paints could be filled with
nickel, copper, or silver particles (I have yet to see one with gold
filler but in for an ounce, in for a pound).  As the paint ages an oxide
forms on the surface of the metal particles.  That increases the paint's
sheet resistivity and degrades the its performance.  Copper oxides are
more resistive compared to silver and nickel and for that reason all EMI
shielding paints use silver or nickel, usually in the form of Ni or Ag
plated cheaper substrates in a cost reduction ploy.  The substrates
chosen include copper, glass, and graphite in powder, sphere, or fiber
form.  There was a project at Battelle Memorial Institute attempting to use a
modified aluminum and we found that aging copper and aluminum filled
materials made them useless.  The best were the most expensive materials
(go figure) including silver and nickel plated copper powder and
similarly metalized graphite fibers.  Lab plaques of these
configurations tested about the same initially.  However later testing
showed that wide variations in temperature and strong mechanical shock
could degrade performance.  This seemed to be due to microfissures being
formed in the film layer.  Two years ago I dug out some old test results and discussed the
alternatives with Avidyne nee Ryan.  Their experience has demonstrated
similar performance in the real world, i.e. the silver paint worked fine
initially but a couple years of use showed a gradual reduction in
effectiveness.  Ryan suggested aluminum or copper foil.  I chose Ni plated graphite fiber fabric to test.  We laid up plaques and
sent to an open field site for evaluation.  The results were very
similar in effectiveness to sheet aluminum.  Based on experience that
showed aging would not be a major concern, I went this route by making a
2-veil metallized graphite lay up over the graphite fuselage, which was
then covered with micro and faired in.  So far it seems to work fine.  Robert M. Simon
ES-P N301ES

________________________________

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of
Tom Gourley
Sent: Tuesday, March 06, 2007 2:52 AM
To: lml@lancaironline.net
Subject: [LML] Re: Ground-plane


1.) The counterpoise should be either aluminum, copper, or gold.

2.) Actually silver has the highest conductivity of all metals, which is
probably why it's used to plate the center conductor of some coax cable;